1. Field of the Invention
This invention relates to new and useful acid-curing resin compositions for use in the formation of sand cores and molds for foundry operations and to new di-esters of lower aliphatic dibasic acids.
2. Description of the Prior Art
In the foundry industry, sand is coated with resin binders and formed into molds and cores for the production of precision castings. A wide variety of techniques have been developed for the manufacture of sand cores and molds. These involve the hot box technique for mold and core formation; the shell method; the "No-Bake", and the cold-box technique.
In the hot box and shell methods, sand molds and cores are formed by heating a mixture of sand and a thermosetting resin at a temperature of about 300.degree.-600.degree. F. in contact with patterns which produce the desired shape for the mold or core. The resin is polymerized and a core or mold is formed. Procedures of this type are described in Dunn U.S. Pat. No. 3,059,297 and Brown U.S. Pat. No. 3,020,609.
A particular disadvantage of the hot box and shell methods is the necessity for heating the pattern boxes to 300.degree.-600.degree. F. to polymerize and cure the resin binder. This involves considerable expense and is generally a high cost technique.
The cold box techniques for core and mold formation involve the use of sand mixed or coated with resins which may be cured at room temperature by acid or base catalysis. Acidic or basic catalysts have been used in liquid, solid or gaseous form. Typical cold box processes are shown in Blaies U.S. Pat. No. 3,008,205; Dunn U.S. Pat. No. 3,059,297; Peters U.S. Pat. No. 3,108,340; Kottke U.S. Pat. No. 3,145,438; Brown U.S. Pat. No. 3,184,814; Robins U.S. Pat. No. 3,639,654; Australian Pat. No. 453,160 and British Pat. No. 1,225,984. Many of these processes involve the use of sulfur-containing acid catalysts such as benzene sulfonic acid, toluene sulfonic acid and the like. Richard U.S. Pat. No. 3,879,339 discloses coating sand with an organic peroxide and resin, forming into a mold or core and gassing with sulfur dioxide.
A number of U.S. and foreign patents disclose the use of furfuryl alcohol and other furfuryl-substituted compounds in resin polymerization and also the use of dibasic acids and some esters in resin compositions.
Bradley U.S. Pat. No. 2,238,030 discloses the use of di-alkenyl esters of dibasic acids in the copolymerization of addition polymers.
Dannenberg U.S. Pat. No. 2,650,211 discloses polymers including dibasic acids as precursors.
Treat U.S. Pat. No. 2,999,829 discloses the copolymerization of furfuryl alcohol and maleic anhydride in the prepatatio of foundry cores.
Case U.S. Pat. No. 3,312,650 resins bases on phenol and furfuryl alcohol modified with formaldehyde and treated with an acid catalyst.
Kirkpatrick U.S. Pat. No. 3,244,770 discloses the use of di-esters of dibasic acids in phenolic resin compositions.
Bean U.S. Pat. No. 3,248,276 discloses the use of dibasic acids in resin compositions containing condensation-type resins.
Guyer U.S. Pat. No.3,404,118 discloses the use of furfuryl glycidyl ether in molding resins.
Fitko U.S. Pat. No. 3,600,290 discloses the use of unsaturated esters in resin compositions.
Adkins U.S. Pat. No. 3,725,333 discloses the preparation of foundry molds, etc. using phenolic resins modified with furfuryl alcohol.
Laitar U.S. Pat. No. 4,051,301 discloses resins for sand cores or molds by incorporating furan into a furfuryl alcohol-modifed phenolic resin prepolymer.
Anderson U.S. Pat. No. 4,083,817 discloses the acid curing of mixtures of furan-formaldehyde resins with phenolic resins for production of foundry cores and molds.
British Pat. Nos. 626,763 and 992,345 disclose the use of glyceryl esters and other esters of aliphatic dibasic acids in condensation polymers.
The bis(tetrahydrofurfuryl) ester of adipic acid is known but does not undergo condensation type polymerization.
The above noted patents, however, do not consider the problem of the preferential polymerization of furfuryl alcohol when admixed with phenolic and other condensation-type resins and the problem of short bench life, or any way to overcome these problems.